1. Field of the Invention
The present invention is directed to an x-ray diagnostics installation having a mean image brightness detector, and in particular to such an installation wherein the detector is formed by a matrix of detector elements, and having a control unit to select predetermined elements for signal generation.
2. Description of the Prior Art
X-ray diagnostics systems are known which include a mean image brightness detector. It is also known to form the detector of a matrix of detector elements. Detectors of this type are used in an automatic exposure control loop for recording an image or for transillumination. The mean image brightness in a region corresponding to the organ or body part of which an image is to be generated must be measured and maintained constant. It is known for this purpose to provide a fixed number of measuring fields within the detector by using a matrix of semiconductor detector elements. Arbitrary measuring field shapes can then be achieved by selectively activating individual detector elements. This also permits a rapid change in the measuring field shape to be made. It is also possible to differently weight the output signals of the selected detector elements.
For the best exposure, the selected measuring field must be adapted as closely as possible to the body part of which an image is be obtained.